On Fri, Aug 07, 2015 at 02:35:45PM +0200, Sebastian Andrzej Siewior wrote: > On 08/07/2015 12:55 PM, Russell King - ARM Linux wrote: > > On Fri, Aug 07, 2015 at 10:41:57AM +0200, Sebastian Andrzej Siewior wrote: > >> This DMA driver is used by 8250-omap on DRA7-evm. There is one > >> requirement that is to pause a transfer. This is currently used on the RX > >> side. It is possible that the UART HW aborted the RX (UART's RX-timeout) > >> but the DMA controller starts the transfer shortly after. > >> Before we can manually purge the FIFO we need to pause the transfer, > >> check how many bytes it already received and terminate the transfer > >> without it making any progress. > >> > >> >From testing on the TX side it seems that it is possible that we invoke > >> pause once the transfer has completed which is indicated by the missing > >> CCR_ENABLE bit but before the interrupt has been noticed. In that case the > >> interrupt will come even after disabling it. > > > > How do you cope with the OMAP DMA hardware clearing its FIFO when you > > pause it? > > I don't ... and so you introduce a silent data loss bug into the driver. That's not very clever. > Right now the 820-omap (8250-dma in general, too but they don't use > this driver) pause only the RX transfer in an error condition. This > means it is only device-to-mem transfer. I only mentioned the TX > transfer here since this was easier to test. That may be how 8250 works, but 8250 is not everything. You can't ignore this problem. You have to deal with it - either by not allowing a channel that would loose data to be paused, or by recovering from that condition. You're not doing either in your patch. Therefore, I have no other option but to NAK your change. Sorry. Please fix this. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
